1. Field of the Invention
The invention relates generally to solid waste disposal and particularly to disposal of solid municipal waste by pyrolytic treatment.
2. Description of the Prior Art
Liquid and solid waste disposal has become a particularly acute problem in urban areas due to population density patterns and air and water quality considerations. Longused methods of municipal waste disposal have become increasingly less satisfactory as available land near urban centers has virtually disappeared due to population pressures, and as air and water quality considerations have lessened the attractiveness of waste incineration practices.
A widely employed method for the disposal of solid municipal waste is the "land-fill" procedure which involves mixing of the waste with soil and the eventual covering over of the waste with a top layer of earth. Problems now being encountered with such prior practices include the vanishing availability of suitable land-fill sites within reasonable distances of urban areas. The terrain of suitable land-fill sites must be such that the waste can be covered over. Even when such sites are available in an urban area, citizen resistance to the location of a landfill near human habitation is increasingly strident. The siting of land-fills outside of the urban area can result in inordinate expenses for transport of the waste to the land-fill site as energy costs increasingly become a major factor. Of further concern is the fact that the disposal of waste in a land-fill has often proven to be hazardous due to the nature of the waste or due to uneven settling of the land-fill site which prevents previously intended conversion of the site to other uses.
The most widely used alternative to land-fill waste disposal is incineration, typically in forced air incinerators. Incineration, due to the necessity of handling large volumes of gases bearing combustion products, results in pollution of the atmosphere. When incineration is carried out in the urban area itself, as is usually the case due to the need to locate a waste disposal system near the source of the waste, air quality within the urban area is adversely affected. Removal of pollutants from the gases issuing from such incinerators cannot be practically accomplished, even partial removal being costly.
The disadvantages of land-fill and incineration methods have shown the need for alternate waste disposal methods. A technique generally referred to as pyrolysis holds the promise for relatively pollution-free and odor-free treatment of solid municipal waste. The solid residue resulting from a pyrolysis process is typically non-putrefiable and non-pathogenic, thereby facilitating disposal of the "ash" or "char" which results from such processes.
Even though pyrolysis techniques offer a number of theoretical advantages, pyrolysis waste disposal systems have not achieved widespread commercial use. This failure of pyrolysis technology to achieve a clearly acceptable status in the art involves at least in part certain heat transfer problems and the tendency of such systems to form "slag" in the pyrolysis chamber. In order to produce substantially odor-free end products, it is necessary to heat the decomposition products to a temperature which approaches that temperature at which slagging is encountered. However, if the temperature in the pyrolysis chamber is allowed to rise above this slagging temperature, glass and other inorganic materials melt to form a tenaciously adhering slag over all surfaces exposed to the waste. This slag actually "freezes" the pyrolysis apparatus and can only be removed by extremely tedious mechanical methods. One advantage of the present pyrolysis system is the ability to effectively heat the decomposable waste in an efficient manner such that the temperature within the pyrolysis chamber can be more readily controlled.